如何绘制CIImage（或者可能CVPixelBuffer是，但我想添加文本更容易CIImage）？不是 UIImage
AVAssetWriter我使用和CMSampleBuffer（来自视频、音频输入）录制视频（.mp4 文件）。在录制时我想在视频帧上添加文本，我已经转换CMSampleBuffer为CIImage，现在我需要以某种方式添加文本CIImage并转换回CVPixelBuffer. 我真的没有在 Swift 中找到任何简单的示例，如何添加（绘制）文本CIImage或添加任何其他内容（如线条、矩形，而不仅仅是文本）。
/// encode video buffer
func appendVideoSampleBuffer(_ sampleBuffer: CMSampleBuffer) {
// before encoding video frames into a file I would like process it
// 1. convert CMSampleBuffer to ciImage
let cvPixelBuffer: CVPixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
let ciimage : CIImage = CIImage(cvPixelBuffer: cvPixelBuffer)
// 2. do something with CIImage
// 3. convert CIImage back to CMSampleBuffer
let sampleBufferWithText == ...
appendSampleBuffer(sampleBufferWithText, ofMediaType: AVMediaType.video.rawValue)
}
/// encode audio buffer
func appendAudioSampleBuffer(_ sampleBuffer: CMSampleBuffer) {
appendSampleBuffer(sampleBuffer, ofMediaType: AVMediaType.audio.rawValue)
}